Item Audio "Spoke" for the Linn LP12 anybody..?

[sq225917]

Whichever way you look at it it's a bodge at best which introduces as many issues as it ameliorates. While it may ostensibly resemble a panhard rod these spokes are equally flexy in all directions and do not have the restricted axis of rotation that a true panhard rod provides.

They will increase and decrease in length, imparting torque, with the vertical bounce of the deck, adding exactly what they are designed to remove. They will reduce the compliance and affect the resonant frequency of the vertical component of the suspension of the deck.

They will also short circuit the suspension and couple the motor noise via the top plate directly to the sub-chassis. In fact what better to do this than 3 rigid spars.

It's a nice idea, but i'd much rather just have suspension bolts with much larger, flatter heads and suspension springs that are wound twice as wide to limit sideways movement of the subchassis with 'zero' adverse effects.

 

[YNWOAN]

It's the classic panhard rod concept. Regardless of its operational simplicity, I strongly suspect that springs with opposing 'twist' will still need tuning-in to optimise the vertical bounce and for the LP12 magic to surface.

It's not 'magic', but the LP12 springs do have to be rotated to achieve correct alignment and bounce; there are two reasons for this 1/ the two ends of the springs are not entirely parallel (despite being ground flat) and, 2/ the centres of the spring ends vary in terms of vertical axis alignment.

 

[bottleneck]

Is the LP12 really this complicated?

Can't it just be left alone and have records spun upon it?



(confused simpleton NAS user)

 

[YNWOAN]

No, it isn't complicated, it only has to be done the once - not every time you use it!

 

[djftw]

Its already been done (sort of) and is called the funk kit. Ok it isn't a radikal motor its Arthur's own but its a definite upgrade.

How good VFM any of the LP12 upgrades are is in my view questionable. My new orbe/graham cost less than any of the rated ones, leaves my 2001 LP12 in the dust and I've got a whole TT not just a couple of bits for the old one.

Lol, thought it was too obvious for someone not to have tried it! In 'Ankhor Link Kit' for with the vector drive pulleys etc. it seems very well thought out - though considering the extent of the modifications they have made elsewhere I'm a little surprised that they haven't changed the suspension configuration to spread the weight more evenly between the suspension springs. I would have thought was something worth considering if making a sub-chassis that required it's own top plate (or extensive modification of an existing one I suppose), why be bound by Linn's suspension lay out? I can't believe that the current configuration is optimum. The choice of carbon fibre for the top plate also seems counter-intuitive to me, but I suppose if the electromagnetic noise on the DC motor is very low it makes sense. Also a means of adjusting the suspension from the top plate would be nice!

That said where do you stop! You really do have a point. My current LP12 was something of a second hand bargain, and whilst I wouldn't really hesitate to invest in upgrading or replacing my arm if I had the funds, as it is transferable to another deck, I must admit I'm a bit less sure about things like upgrading the sub-chassis, with the possible exceptions of the Sole/Vivid/Cetech their price seems to exceed the 2nd hand value of the basic TT (i.e. sans Power Supply, Arm & Cartridge) and even those exceptions are around the sort of price a savvy buyer with a bit of patience would pay for a pre-cirkus black-ash example. That's not to detract from any of them, but there must come a point when regardless of your prior investment in the deck, the performance gain just can't justify the expenditure next to the option of selling up and buying a different deck that doesn't have some of the LP12s problems!

That said, I love my LP12 and can fully understand why some people throw so much money at them. There's also a lot of advantages in owning a product with the market longevity and reputation of the Sondek, especially for a 2nd hand buyer. It's a shame that there isn't really a modern deck especially like it, if I owned Linn right now I would be asking my engineers for 'Son of Sondek'; a complete redesign free of some of the inherent flaws and eccentricities born of the original design having to compensate for problems like motor noise, but retaining the principle of a floating sub-chassis and other things about the original that made it a good deck. Hell it could even be direct drive - Ivor has been quoted as saying that if he knew how popular it would have been then it would have been DD! If it could be backwards compatible with the old version - great! But starting from the point that it must be seems to involve quite a bit of compromise and you could always cut the price of the old one and continue to sell it, together with all the upgrades and accessories, and put in place an exchange programme to maintain the upgrade path/hierarchy and avoid pissing off your loyal customers too much!

 

[YNWOAN]

Mark (and Andrew), How about a Rubikon with a mount for the Radical motor? That would seem the obvious solution to me - if Linn's spiel about the Radical is not overly influenced by the marketing department it seems to me that the motor should, in addition to the claims they make, be quiet enough that any remaining advantage of having the motor isolated from the sub-chassis would be outweighed by disadvantages of the rotational pull on the suspension. Some top plate modification might be needed to accommodate that too I guess. I imagine radical owners interested in a non-Linn sub-chassis would be a small market thought...

Hmm..I may seem like a good idea but there are a number of issues to consider:

1/ I don't think the motor (or any motor) is quiet enough to mount directly to the chassis. Linn's claims regarding how quiet the Radikal motor is largely centre on its electrical characteristics - not the mechanical ones.

2/ The extra weight of the motor would have to be taken into account.

3/ The change to the centre of gravity of the chassis would have to be accounted for.

4/ A new top-plate, and even a new belt, may be needed depending on decisions made regarding weight distribution, position etc.

 

[sonddek]

Whichever way you look at it it's a bodge at best which introduces as many issues as it ameliorates.

Let's face it, the whole deck is a bodge. They've only recently unbodged the three screws which hold a pressed steel chassis to a woodchip arm board. Many very successful machines are bodges. Soyuz, for instance.

While it may ostensibly resemble a panhard rod these spokes are equally flexy in all directions...

This is false. The spokes will not stretch or compress much along their own axes because they are made from a stiff material. Their resistance in that direction will have the effect of obstructing rotation of the subchassis very effectively. As can be seen in the photo, the rods are arranged tangentially to platter rotation, and they are at about 120 degrees to each other, making rotation of subchassis relative to motor in the vertical axis all but impossible. Their resistance to bounce will be poor because they are long enough to accommodate bending. Simply imagine how hard it is to bend the rod, and then imagine stretching the rod by the same distance. The required forces would be several orders of magnitude apart.

They will increase and decrease in length, imparting torque, with the vertical bounce of the deck, adding exactly what they are designed to remove.

As I pointed out above, that won't be audible since the deck does not bounce during use, therefore that effect is negligible, unlike the subchassis rotation which will be obstructed. Subchassis rotation can be seen with the naked eye every time you switch on the deck. The bounce is not the purpose of the springs. They are there to isolate.

They will reduce the compliance and affect the resonant frequency of the vertical component of the suspension of the deck.

That is certainly true but may not be very important. Contrary to popular belief, the purpose of the suspension is to isolate the subchassis from acoustic feedback, not to make it bounce prettily. They are not necessarily the same thing.

They will also short circuit the suspension and couple the motor noise via the top plate directly to the sub-chassis. In fact what better to do this than 3 rigid spars.

The top-plate, in so far as it is free to move at all, probably resolves most of the absorbed motor vibration into vertical movement, because it is fixed at its edges to a larger mass, like a drum. As a result, the top-plate's movement is in exactly the wrong axis to be successfully transferred by the rods. The top-plate vibrates vertically, but the rods allow movement in that direction. As such, the rods may not be a very good way to get top-plate vibration into the sub-chassis.

It's a nice idea, but i'd much rather just have suspension bolts with much larger, flatter heads and suspension springs that are wound twice as wide to limit sideways movement of the subchassis with 'zero' adverse effects.

That would also increase the resonant frequency, and reduce the ability to isolate, while making little difference to the ability of the spring to shift laterally. The springs are quite good elastic energy stores of lateral torque. Simply making them broader won't fix that.

 

[djftw]

Hmm..I may seem like a good idea but there are a number of issues to consider:

1/ I don't think the motor (or any motor) is quiet enough to mount directly to the chassis. Linn's claims regarding how quiet the Radikal motor is largely centre on its electrical characteristics - not the mechanical ones.

2/ The extra weight of the motor would have to be taken into account.

3/ The change to the centre of gravity of the chassis would have to be accounted for.

4/ A new top-plate, and even a new belt, may be needed depending on decisions made regarding weight distribution, position etc.

I see! I really don't know how exactly one would go about it, but there must be a way for the motor to be supported by and move with the sub-chassis, but be isolated from it at audio frequencies? Things like the Rega's better offerings which so far as I can tell still have the motor, bearing and arm all attached to the plinth don't seem to suffer especially from mechanical motor noise - ditto some DD decks. I can't imagine that there isn't a way of implementing something similar in a suspended deck - and without wanting to sound sycophantic, if I won the lottery and decided I wanted to bring a TT to market you would be someone I would want on my team, precisely because that is the sort of thing that I get the decided impression that given the time and resources you could work out!

As for the last three it seems to me that all of those could actually be accounted for within the design of the sub-chassis - excepting that the installer may still need to enlarge the hole for the motor spindle in the top plate to avoid fouling! But even with a demand for a new belt - that should surely be relatively straightforward and inexpensive to source (at least in bulk), the stock Linn belt isn't exactly anything special is it? And as a new hole in the top plate would just need to give enough clearance for whatever is going through it as the suspension moves - it doesn't exactly need to be precision engineered, just a sharp drill bit and a bit of care!

 

[sonddek]

I see! I really don't know how exactly one would go about it, but there must be a way for the motor to be supported by and move with the sub-chassis, but be isolated from it at audio frequencies? Things like the Rega's better offerings which so far as I can tell still have the motor, bearing and arm all attached to the plinth don't seem to suffer especially from mechanical motor noise - ditto some DD decks. I can't imagine that there isn't a way of implementing something similar in a suspended deck - and without wanting to sound sycophantic, if I won the lottery and decided I wanted to bring a TT to market you would be someone I would want on my team, precisely because that is the sort of thing that I get the decided impression that given the time and resources you could work out!

As for the last three it seems to me that all of those could actually be accounted for within the design of the sub-chassis - excepting that the installer may still need to enlarge the hole for the motor spindle in the top plate to avoid fouling!

You still have the problem of the elastic belt to deal with.

I would like to take a Technics 1210 motor and glue it onto a Sondek subchassis, while gluing the magnet to the sub-platter. A big hole would need to be cut into the top-plate. This way you would really cut out the elastic wells, benefit from the Sondek's isolation, while harnessing the Technics' ability to keep the platter spinning at correct speed. Frankly Linn should have produced a deck like this long ago, considering Ivor's direct-drive comments, but they seem to prefer milking the installed base of Sondek users.

Meanwhile this spoke idea looks like one of very few efforts to properly address the problems in the Sondek design. Whether it works or not will no doubt be open to fierce debate. I think the main thing to listen for will be improved pitch accuracy, although detriment to noise floor may also be noticeable.

 

[YNWOAN]

Actually, new belts are not that easy, or cheap to source - one would be expected to buy quite a lot of them too.

To be honest, I have looked into these issues and the rotation of the chassis - the impact of this later aspect is overplayed in my opinion, and introducing methods of potentially curing it are apt to introduce more issues than they resolve.

 

[pure sound]

Besides Pink Triangle with the Anniversary, this is what Fons were trying to do back in the 70's. The problem is that close coupling the motor to the platter at audio frequencies is what you want so trying to de-couple the motor from the subchassis at those frequencies defeats the object of & benefits accruing from mounting it there. The only option seems to be the use of a very weedy but quieter motor which still needs some compliance (slop) in its mounting arrangement.

I'd also argue that I've yet to hear a 'fixed' plinth or DD deck that offers the same subjective S/N performance as a well executed suspended deck which has the suspended part effectively decoupled from the motor & its inherent mechanical noise. They can do some things better; bass, pitch stability etc but not everything.

I use an SP10 mounted in a very substantial plinth which stands on a sprung suspension. It is very well isolated from the outside world. However I'm still not convinced that the SP10's motor doesn't create some noise even at a very, low level which has the effect of masking the finest detail.

 

[AndyU]

It's still not bad for a copy of a Thorens 150 knocked up in his dad's precision engineering company by a young hi-fi enthusiast that failed to complete an engineering course at a mediocre university.

 

[pure sound]

Not to go over the same old ground yet again, but it's fairly well established that 'his Dad's engineering company' were already making this deck to the design of someone else and it was called an Ariston RD11.

 

[AndyU]

opionions vary .. some people think that the 'someone else' just sold the RD11 thing and kidded on that he designed it ..

 

[John]

I wouldn't be too keen on butchering my LP12 to try such a modification. Chances of finding a like equipped LP12 to mine to compare against that has had the procedure performed is highly unlikely so it's a non-starter for me.

I also fail to hear the pitch problems detractors write about regarding the LP12, so I will just go on enjoying my tunes. I anxiously await being blown away by a needle drop comparison of something better, but haven't.

 

[pure sound]

I'd be very surprised if you were ever to be 'blown away' by a needle drop. I certainly wouldn't use them to make an absolute assessment of any actual turntable. You can sometimes glean a flavour & sometimes hear problems with a deck/cartridge or recording method. But that's about it. What has become apparent to me is that some decks end up being 'voiced' to suit the subsequent system they are used with. That voicing doesn't always transfer well to another set of amplification & speakers in a different room. The chances are that the only deck & phono stage you'll really like (by needledrop) would be one that has a similar character to what you already use.

 

[John]

If pitch problems are as apparent as detractors say they are, I would think they would be apparent via needle drops. I find the needle drops pretty telling of changes I have heard "live", and don't discount them. I listen to the needle drops via headphones which reveal differences I listen for quite effectively IMO.

 

[AndyU]

Don't forget that this mod is sold by a company who also sell bituminously damped and cryogenically treated laptops.

 

[sq225917]

This is false. The spokes will not stretch or compress much along their own axes because they are made from a stiff material. Their resistance in that direction will have the effect of obstructing rotation of the subchassis very effectively. As can be seen in the photo, the rods are arranged tangentially to platter rotation, and they are at about 120 degrees to each other, making rotation of subchassis relative to motor in the vertical axis all but impossible. Their resistance to bounce will be poor because they are long enough to accommodate bending. Simply imagine how hard it is to bend the rod, and then imagine stretching the rod by the same distance. The required forces would be several orders of magnitude apart.

You still don't get it do you, the sub-chassis never pivots about the centre of the bearing under only torsional load along a single rotational axis aligned through the middle of the bearing, simply because that point isn't the geometric centre of the suspended parts of the deck or the COG for these parts.

Secondly, the motor is positioned off to one side of the suspended assembly and the drive vectors of the force transmitted to the sub-chassis from the motor actually pretty much come from the centre of the motor itself. So in reality the sub-chassis swings fore and aft from centre of the motor but in directions constrained by the compliance of the suspension and tonearm wire.

The reality is there is no rotational motion about the bearing, more like a crooked pendulum loosely based about the motor position.

 

[sonddek]

You still don't get it do you, the sub-chassis never pivots about the centre of the bearing under only torsional load along a single rotational axis aligned through the middle of the bearing...

Please show me where I stated that the subchassis rotated around a vertical axis "aligned through the middle of the bearing". There's no point telling me that I "still don't get it" when you aren't able to accurately read what I've actually written. Maybe in subsequent posts you can find a happier turn of phrase than "You still don't get it, do you...".

You are quite right that there is a sideways force on the subchassis when the motor applies torque, but it seems to me that this spoke modification will go some way towards stabilising that movement too.